Generally, catalytic production of hydrogen from hydrocarbon material is a two-step steam reforming process. A gaseous or liquid hydrocarbon feed stream is contacted with a catalyst and steam at high temperature, producing hydrogen, carbon monoxide, and carbon dioxide. These products are then cooled and contacted with a shift conversion catalyst which promotes reaction of the carbon monoxide with steam, producing additional hydrogen and carbon dioxide.
Prior to steam reforming, the hydrocarbon material is generally desulfurized to prevent poisoning of the catalytic surfaces. While steam reforming can still be affected with the poisoned catalyst, catalytic activity is reduced by several orders of magnitude. Generally, steam reformers are operate at higher temperatures to partially compensate for this reduced activity. This significantly increases energy requirements while accelerating catalytic decay.
Various processes exist for desulfurizing a hydrocarbon material. One desulfurization process involves treating with hydrogen in the presence of a hydrodesulfurization catalyst. This converts any sulfur in the hydrocarbon feed stream to hydrogen sulfide which is readily removed by adsorption on zinc oxide. However, such a process cannot be used to desulfurize heavier distillate fuels such as No. 2 fuel oil. Such fuels are therefore not considered suitable fuels for steam reforming.
In commonly owned U.S. Pat. No. 4,414,140, issued to H. J. Setzer, high activity sulfur tolerant steam reforming catalysts are described comprising rhodium or nickel supported on lanthanum stabilized alumina or magnesium promoted lanthanum stabilized alumina. In commonly owned U.S. Pat. No. 4,503,029, issued to H. J. Setzer, the improved steam reforming processes, utilizing the above catalysts, are described. While such catalysts have been successfully employed, the search continues for catalysts which achieve even higher activities with improved sulfur tolerance.